Spark plug



Aug. 15, 1950 E. w. MITCHEL SPARK PLUG Filed April 22, 1946 mmmmmm 4 \IQI 14/45 70? awn: M Maw .64.

Patented Aug. 15, 1950 SPARK PLUG Edward W. Mitchel, Detroit, Mich., assignor to Hiram W. Broadwell, Detroit, Mich.

Application April 22, 1946, SerialNo. 663,883

2 Claims. 1

My invention relates to a new and useful improvement in a spark plug and adapted for use in internal combustion engines and has for its object the provision of a spark plug which will be simple in structure, economical to manufacture, durable, and highly efficient in use.

Another object of the invention is the provision of a spark plug so constructed and arranged that the operation of the plug is not controlled by the heat range which is true of conventional spark plugs now inuse. The present invention provides a spark plug which, in its operation, depends on the turbulence of the gas effected by the internal construction of the plug.

()ther objects will appear in the description which follows:

It is recognized that various modifications and changes may be made in the detail of structure illustrated without departing from the invention itself and it is intended that such shall be em braced within the scope of the claims which form a part hereof.

Forming a part of ings in which:

Fig. l is a longitudinal, vertical, central, sectional view of the invention, 1

Fig. 2 is a fragmentary, central, sectional view of a slight modification,

Fig. 3 is a central, sectional view of a further slight modification,

Fig. 4 is a fragmentary central, sectional view showing further modification,

Fig. 5 is an endviewof the plug;

In the drawings'l have illustrated the spark this specification are drawplug as comprising a metallic shell 9 which is inserted into the cylinder block it] which is provided with the cylinder 56 in which'is slidably mounted the piston M. Engaging in one end of the shell 9 isthe insulating member I l having the bore 82 formed therethrough opening into a 2 s In use the sparking would be between the edges of the portion H! at the end of the passage 2| and the edges of the disc 2-3 at the edges of the passage 48.

A jam nut 2 is threaded into the shell 9 and presses the gasket 25 against the shoulder of the core or insulating member II. This forces the insulating member H into close contact with the washers 2.2 and thus there is provided a structure which is leak-proof against the compressed gases. In operation the piston 41 will compress the gases forcing the same to flow through the passage 48 into the chamber 26]. When the gas is ignited by the spark the combustible mixture, which is in the passage 48, the passage 2 l and the chamber ill, will ignite. It is preferred that the chamber 29 be circular in cross section. When this takes place there is a discharge of fiame intio the cylinder 45. The passage 48 is considerably smaller in diameter than the chamber 20 but of greater length than the diameter of the chamber pocket or chamber i3. Extending through the bore I2 is therod orelectrocle i l on which is threaded the nut it to secure the terminal lug It of the cable ll in contact with the rod or electrode M.

The rod Hi is provided with a head It to which is attached the shell til-having a charm her at formed therein opening to a constricted passage-way 2|. The 'rod and shell may be, if desired, formed of a single piece of material with the end turned in to form the restricted passage formed in the shell 2| after the bore 29 has been Id. The core of the spark plugembodying the insulating member it rests upon the insulating washer 22 which, in turn, rests upon the metal ring 23 positioned in the bottom of the shell 9.

20 so that there is a constricted outlet passage through which the ignited gases in the chamber 20 may pass. This produces a sort of jet action which effects a spreading'of'the flame throughthe compressed gases in the upper end of the cylinder resulting in quicker ignition of these gases, higher degree of efiiciency particularly in .increas ing speeds of a vehicle and-in economy in consumption of fuel.

With sparkplugs as'noW constructed; the spark plug is adapted for a certain. heat range and the spark plugs are classified as cold, medium orhot, depending on the'heat range with which theyare intended to be used. To provide these plugsof different heat range the plugs are constructed with various thicknesses ofainsulation about the central electrode. The purpose is to provide a, spark plug so insulatecl that it willbecome hot enough to prevent carbon formation thereon. Consequently, the slark plug to be used will de pend upon the motor with which it is to housed, the use to which the motor is to be put and in general the heat developed by the engine. In plugs as now constructed there is a gap or space between the metal shell and the insulation. to which carbon can and-does adhere. The present 1 invention eliminates this space so that no. space is provided in whichcarbon can form or. adhere to the'insulation. With a. spark plug constructed according to the present invention attention need not be given toany heat range as the, present plug is adapted forall heat ranges and isnot effected in its efiiciency and operation by avaria tion of heat of the engine. This is so primarily because of the turbulence created by the passage of the gas into and out of the chamber 23 and this turbulence remains substantially uniform regardless as to the heat developed.

Another problem in spark plug construction is to provide a spark plug that will not leak gas. Where the stem M is passed through the porcelain insulating core I! it is difficult to maintain a construction which is leak-proof against the gas because of the variation of expansion and contraction of the metal and porcelain parts. The amount of heat used in the operation of the engine, which is sufiicient to keep the conventional type of spark plug clean along the insulation or porcelain, loosens the porcelain and causes a leak, thus shortening the life of the spark plu and reducing the efficiency of the engine. There is also a loosening of the connection between the porcelain and metal shell sufficient to cause leakage which resu ts from variance in expansion and contraction. The present invention does not get as hot as the conventional heat range type of spark plug and, therefore, a larger part of contact for sealing may be used and not be affected by the expansion or contraction. Another advantage so far as leak-proofing is concerned is that in the present invention a very small portion of the insulator is exposed to the pressure of the cylinder and this is not true of the conventional type of spark plugs. That in the present invention the insulation is not directly exposed to the explosion or combustion pressure as in conventional plugs now in use. but only indirectly from any expansion of shell l9 and the head is by the pressure in chamber 20.

Another objectional feature to be overcome in the fabrication of spark plugs and in their opera tion relates to the spark gap. It is important that this spark gap remain at a permanent predetermined set distance and that this gap be maintained during the operation of the spark plug. In the present invention this is accomplished as the gap is established when the spark plug is assembled and this gap is so constructed as to be shielded from the impulse of the explod ng gas more than the o en type of points. It has also been noted that the wearing of the sparking points is not effected alone by the action of the spark but that there is a wear resulting from a gas wash. This gas wash is the passing of the gases across the sparking points. In the present invention this is avoided because the sparking parts are not open to the gases which are moving about in the cylinder 56.

Various size gaps may be easilv obtained with a spark plug constructed in this manner. In Fig. 2 I have shown a sl ght modification in which the shell 26 is provided with the space 2'! in which the insulating core 28 is positioned and held in position bv the jam nut 23a. This insulating core is provided with the electrode 54a having the head [So constructed as for IS. The washer 22 and the r ng 23 shown in Fig. 1, have been removed from the assemblv shown in Fig. 2.

In Fig. 3, I ha e shown a, slight modification in which I have inserted, between the insulating core 3'! and the bottom of the shell 29, a metallic ring 36 and insula ing washers 35 and 31. The metallic r ng 36 is further insulated from shell 29 by insulating ring 65. The electrode 33 is provided with a head 34 and the jam nut bears up against the sealing member 32. In this construction the sparking would be through the central passage formed in the washers 35 and 3! 4 and the ring 36. Should a short circuit take place between the member 34 and the ring 36 the spark then would jump from the ring 36 to shell 29 and if a short develops between the ring 35 and the shell 29 then the sparking would, of course, be from member 34 to ring 36.

In Fig. 4, I have illustrated a construction in which the shell 38 receives the porcelain insulator 39 and through which is extended the electrode 40 having a head M. This head H is spaced from the bottom of the shell 38 by an insulating washer 42. It is believed obvious that by removing the insulating washers as shown in Fig. 2, or increasing their number, the gap for sparking may be varied. It will also be noted in Fig. 2, that the head [9a is positioned inwardly slightly from the face of the insulating core 28. By varying this distance the gap may also be varied. However, in all ty es of construction the chamber 29 is provided with the passage 48 communicating therethrough so that the jet action of the flame into the cylinder is obtained While the turbulence which sets up in the chamber 20 is lso present.

In the operation of the engine a certain amount of oil is wiped up along the walls of the cylinder 46 by the piston 41 and as the mixture is com ressed this oil is wiped along the under side of the dome of the compression chamber. To prevent this oil from entering through the passage 48 a downwardly projecting portion 60 is provided on the shell member 9. This projection 50 extends below the top of the dome 6| so that any oil previously thereon would be deflected downwardly and onlv combustible gases would pass through the pas age 48. In Fig. 2, projection a is shown with a concave side wall 61 which tends to further eliminate any oil from enterng into the spark plug.

Experience has shown that a spark plug constructed in this manner is highly eflicient particularly in fuel economy and speed in pick-up of an engine.

It will be noted that there are five characteristic features of the present invention which have been mentioned. First, an explosive chamber having two or more sizes of passages leading thereto and therefrom is used which creates a turbulence within the plug itself and which serves to clean the sparking area. Secondly, a chamber within the spark plug having a passage leading thereinto and therefrom of a uniform size may be used and in such instance the turbulence of the gases which is set up in the cylinder serves to kee the points clean. Third, the sparking gap is so located within the chamber that a comparatively small percentage of the combustible gases contact or pass the sparking poin s thus elimin ting corrosion caused by gas wash. Fourth, the chamber into which the mixture of combustible fuel is forced is so located that it fires or explodes within the plug thus ca sing a jet of ignited gas to issue out of the opening of the pl g so as to speed up complete combustion. Fifth, the present invention is so constructed on the lower end with an exten ion beyond the threaded portion so as to extend beyond the cylinder head or free from the cylinder head and so shaped as to protect the opening leading into the chamber within the plug from surplus lubricating oils which are traveling radially or otherwise around the end of the plug thus allowing only combustible gases to enter the plug. These features have proven to render such a plug so constructed highly eflicient.

What I claim as new is:

l. A spark plug of the class described, comprising: a metallic shell adapted for mounting in an engine block and having a cup-shaped portion; a neck projecting outwardly from the face of said cup-shaped portion and provided with a passage therethrough communicating with the interior of said cup-shaped portion; an insulating body mounted in said cup-shaped portion; a metallic electrode extended through said insulating portion; and a hollow head on the inner end of said electrode communicating with the passage through said neck, and in spaced relation to said shell a sufficient distance for effecting sparking thereto; said hollow head being of greater inside diameter than the diameter of said passage and said passage being of greater length than the inside diameter of said head.

2. A spark plug of the class described, comprising: a metallic shell formed cup-shaped at one end; a neck projecting outwardly from the closed end of said shell and having a passage formed therethrough into the interior of said cup-shaped portion; an insulating body mounted in the cupshaped portion of said shell; a metallic electrode projecting through said insulating body; a head formed on the inner end of said electrode and provided with a chamber formed therein communicating with the passage through said neck, said head terminating in spaced relation to said shell for sparking toward the same; said chamber being of greater diameter than the passage through said neck and of a diameter less than the length of the passage through said neck.

EDWARD W. MITCHEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 741,684 Lehman Oct. 20, 1903 1,531,130 Petrus Mar. 24, 1925 1,544,630 Braden July 7, 1925 1,987,612 Fernandez Jan, 15, 1935 2,054,134 Mitchel Sept. 15, 1936 FOREIGN PATENTS Number Country Date 224,812 Great Britain Nov. 20, 1924 

